1. Field of the Invention
The present invention relates to a suspension system for motor vehicles with level regulation for adjusting a predetermined height of the vehicle body which includes at least one piston-cylinder unit with a work cylinder, a piston rod, a damping piston having damping valves, and a pump for an oil reservoir and corresponding inlet and outlet lines between the oil reservoir and the piston-cylinder unit.
2. Description of the Related Art
Suspensions with automatic level regulation for motor vehicles are known, for example, from German reference DE 32 12 433 A1 wherein the suspension units of the vehicle wheels are supplied from a central oil reservoir via correspondingly open hydraulic lines. Corresponding actuating valves connect the suspension units with the oil reservoir and are supplied with an appropriate amount of oil from the oil reservoir by a central pump. A flow regulator and a height sensor act in the oil circuit when needed to adjust the vehicle body to an appropriate height and the pump is activated in response to this flow regulator. A disadvantage in a suspension unit of this type is that hydraulic lines needed for the forward and reverse flow and the pressureless oil reservoirs require maintenance in that the filling level of the damping medium must be constantly monitored. Further, suspension units of this type cannot be retrofitted in an existing vehicle.
It is an object of the invention to provide a suspension system with level regulation which can be controlled and sensed electrically and which is also easily retrofitted in existing motor vehicles.
According to the present invention, the object is met in that a pump comprising a pump piston and a drive unit is arranged such that the pump piston is acted upon on the delivery side and on the driving side by the pressure of the piston-cylinder unit.
In the present invention, the pump piston itself provides for tightness by a close sliding fit. A slight oil leakage that occurs through the sliding fit is guided back to the oil reservoir again.
Since there are no seals acting on the pump piston, startup problems which generally occur from dynamic seals are minor even after long shelf times and with high internal pressure in the device.
The pump piston has a sliding fit relative to the pump cylinder. In this respect, absolute tightness is not required for the piston in the pump cylinder.
In another embodiment, the drive unit is provided with a cam and includes a pressure bearing for supporting a shaft carrying the cam. In this respect, the pressure in the oil reservoir is supported by the pressure bearing of the shaft when the cam is loaded toward the drive. This pressure bearing may comprise a ball bearing, thereby providing a low-friction support. Coated bearing bushes or other friction-reducing bearings may be used on the opposite side of the cam to ensure the lowest possible friction in the drive unit.
According to another embodiment, the pump is sealed relative to the piston-cylinder unit and relative to the atmosphere. Seals which seal statically and seal the housing parts relative to one another may be used for this purpose. This ensures lifetime durability of sealing.
According to yet a further embodiment, the shaft carrying the cam has at least one seal which seals toward the atmosphere.
In another embodiment, the shaft of the cam is sealed toward the atmosphere on both sides. This embodiment may be used when the shaft of the drive unit is to be loaded on both sides simultaneously so that a pressure bearing may be dispensed with.
The diameter of the shaft is approximately identical on both sides of the cam.
According to a further embodiment, a flow connection may extend from the drive side of the pump piston to the oil reservoir. In this respect, the pump piston may be pressure-compensated so that special piston ring seals may be dispensed with and so that leakage oil can easily be guided back to the oil reservoir.
The cam may be surrounded by a sliding ring which is contacted by the pump piston at the end face.
Furthermore, the sliding ring may comprise an external part of a rolling bearing.